JP6348518B2 - Conductive fiber - Google Patents

Description

  The present invention relates to a method for producing conductive fibers for fabrics, a fabric formed from a plurality of such fibers, and an article incorporating said fabric. In particular, the present invention relates to the coating of natural fibers such as cotton using silver nanoparticles. The resulting cotton fabric is seen to be completely covered with silver particles that adhere well to the fibers. Not only is it conductive and extremely flexible, the fabric is also antibacterial because of the presence of nanosilver.

  Some attempts have been made to make conductive cloth so that conductive clothing or travel bags or the like that incorporate electronic devices such as smartphones, GPS devices and personal computers can be manufactured. Such devices have a variety of uses in the consumer, business and military fields.

  Conventional methods for producing conductive fabrics require that conductive filaments be contained within the body of the fabric when the fabric is woven.

  The first conductive fabric was made of silk organza made of silk with conductive fibers wrapped in a thin copper foil (ER Post and M. Orth, IEEE International Symposium on Wearable Computers, October 13). -14, 1997).

  Among fabrics, metal wire or conductive polymer filament blends have also been utilized (H.-C. Chen, K.-C. Lee and J.-H. Lin, Composites, Part A, 35, 1249. -1256, 2004). However, it is difficult to form something other than the simplest design from these processes.

  Another method of producing a conductive fabric is to use a conductive polymer. Conductive polymers are widely used in textile coatings, including polyaniline and polypyrrole (J. Molina, AI del Rio, J. Bonastre and F. Cases, Eur. Polym. J., 45, 1302, 2009). And B. Yue, C. Wang, X. Ding and GG Wallace, Electrochim. Acta, 68, 18-24, 2012). However, these polymers tend to be less conductive than metals.

  A silver-coated nylon cloth is available from Shieldex Trading, Inc. under the Shieldex trademark. It is sold by. This product uses thick silver, is expensive, and is not offered in the form of manufacturing circuits.

  International Publication No. 2008/133672 (Drexel University) discloses a method of grafting multi-wall nanotubes on the outer surface of polyacrylonitrile nanofibers by using a polymer electrolyte as a linker group. No example of any other grafting method is described.

  U.S. Patent Application Publication No. 2007/0054577 (Avloni) includes (i) plasma pretreatment followed by (ii) depositing a conductive coating layer by layer using a polyelectrolyte as a linker group. The formation of electrically conductive fibers is disclosed.

  Chinese Patent No. 102120043 (Basic Medical) discloses the attachment of nano-silver layers to gauze by using chitosan as a linker to make gauze biocidal.

  In addition, WO 00/49219 (Foxwood Research Limited) coats a substrate with biocidal nanosilver by binding silver particles to the substrate using chitosan as a linker group. A method is disclosed. Chitosan needs to be cross-linked to make it insoluble at acidic pH.

In a first aspect of the invention:
(A) providing a fiber having a negative charge on the surface of the fiber;
(B) subjecting the fiber to a material that is not chitosan (hereinafter referred to as a “linker”) to provide a layer of the material on the fiber to change the surface charge of the fiber from negative to positive;
(C) making the surface of the fiber conductive with a metal, wherein the metal of step (c) is provided in the form of metal ions, and the metal ions are reduced to elemental metals; A method for producing a conductive fiber is provided.

  The use of chitosan has been found to adversely affect the physical properties of the fiber, and thus chitosan is excluded from the scope of the method.

  The advantage of providing a metal in the form of metal ions and then reducing is that improved results are obtained (see Comparative Example 5).

  The reducing agent is preferably applied first to the fiber surface, and metal ions are applied second to the fiber surface. The advantage of this method is that the amount of reducing agent and metal ion solution that needs to be used can be minimized and, second, the fibers can be covered with nanoparticles faster.

  In an alternative embodiment, a solution of metal ions, a reducing agent and a linker are first combined (eg, in an aqueous solution) and then this combination is applied to the fiber. In this method, the metal ions are reduced before being applied to the fiber, but the metal ions are also in contact with the linker before contacting the fiber. This method is different from the method in which an elemental metal is applied to a fiber already provided with a linker (compare Example 4 and Comparative Example 5 below). While not wishing to be bound by theory, it is believed that the presence of a linker prevents aggregation of nanoparticles that would otherwise lead to poor results.

  Preferably, the amount of reducing agent used is less than 7 mg (most preferably 6.1 mg) in 98 ml of water. The advantage of this appears to be that the resulting metal particles are unusually small-preferably with an average diameter of less than 50 nm, most preferably about 20 nm. This means that the metal particles are then self-sintered by gently applying heat—for example, silver nanoparticles with an average diameter of about 20 nm are self-sintered at about 60 ° C. to produce fibers. A uniform conductive silver sheath is obtained.

  Next, another metal layer may be applied to the conductive fibers, for example, by conventional electroless plating techniques.

Preferably, the method further comprises after step (a):
(A1) includes a step of treating the fiber (which may use an acidic solution, but preferably with an alkaline solution) to increase the negative charge on the surface of the fiber (so-called “mercelling” step). .

  The fibers may be natural, synthetic, woven or non-woven. Preferably, the fibers are natural fibers and may already be woven into the fabric. Alternatively, the fibers may be woven after being provided in an unwoven form and treated according to the present method.

  Natural fibers (and especially cellulosic fibers such as cotton) inherently have a negative charge on the fiber surface, which is because the metal particles (which form electrostatic bonds for positive net charges) are on the fiber surface. Means not to be bound to.

  The substance of step (b) is preferably a cationic polyelectrolyte, more preferably protamine sulfate, polybrene, poly (L-lysine), poly (allylamine hydrochloride), poly (ethylene glycol-co-dimethylaminoethyl methacrylate) ), Poly (ethyleneimine), polyacrylamide, poly (acrylamide-co-diallyldimethylammonium chloride), diallyldimethylammonium chloride, poly (diallyldimethylammonium chloride), quaternized poly [bis (2-chloroethyl) ether-alt -1,3-bis [3- (dimethylamino) propyl] urea], polyquaternium-7, or any combination thereof.

  Poly (allylamine hydrochloride) is commercially available in two different molecular weights: 1) an average Mw of about 15,000 and 2) an average Mw of about 58,000. Either can be used.

  The amount of substance in step (b) preferably does not exceed 2% by weight, preferably does not exceed 1% by weight, most preferably about 0.2% by weight (specifically 1 g mixed with 100 ml water) A 20 wt% solution of PDADMAC, ie 0.198 wt%).

  In a particularly preferred embodiment, this material is poly (diallyldimethylammonium chloride), also known as PDADMAC (image provided by Sigma-Aldrich):

  PDADMAC plays an important role as a binder between metal and textile, resulting in a more uniform and dense coating. It is believed that the presence of two methyl groups and one amine group in the polymer chain provides an electrically positive site where nucleation occurs. The attachment of PDADMAC to the fiber is thought to be mainly determined by the ionic interaction between the cationic PDADMAC and the anionic surface of the fiber. As a result of its cationic nature, it is believed that PDADMAC adheres to cotton fibers by ionic bonding. Long polymer chains can also provide more cationic sites and possibly more strongly bond to the fabric surface.

Four types of PDADMAC are commercially available and have different molecular weights:
(I) Ultra low molecular weight (average Mw <100,000)
(Ii) Low molecular weight (average Mw 100,000-200,000)
(Iii) Medium molecular weight (average Mw 200,000-350,000)
(Iv) High molecular weight (average Mw 400,000-500,000)
Any of these (or combinations) can be used in the present invention, but (ii) low molecular weight PDADMAC is preferred. Commercially, this PDADMAC is provided in a 20 wt% aqueous solution.

  Step (a1) is a well-known technique known as mercerization. In the conventional mercerization, the concentration of the alkaline solution is 10% by weight or more. However, in the present invention, it is preferred to use about 1% by weight alkaline solution.

  When the fiber is treated with an alkaline solution (such as a sodium hydroxide solution), the number of anionic sites on the fiber surface increases and PDADMAC adsorption is further facilitated.

Sodium hydroxide causes some of the cellulose chains in the fabric to detach, thus increasing the number of negative sites that bind. Thus, increasing the weight percent of NaOH in the solution is expected to increase the number of negative sites. However, it seems that the properties of the fibers change with alkali treatment above 3.0 mold- ³ . Accordingly, in a preferred embodiment, the concentration of the alkaline solution is less than this value.

  Note that other types of alkaline solutions are expected to behave as well. The alkali treatment of cellulose-based materials is called mercerization. However, the surface charge of other types of fabrics can be increased using different treatments.

  The fibers can then be woven into a fabric (or a conductive pattern within another non-conductive fabric). Similarly, the fibers in the fabric can be coated with a conductive coating using the method according to the invention.

  Nano silver coated fabrics can be used in a wide range of applications such as wound dressings, sanitary garments, and medical applications where the presence of bacteria is dangerous. For example, the fabric can be used to make face masks, surgical gloves and military uniforms where wound infections can be seriously affected. High flexibility allows fabrics to be used in the health, leisure and sports industries.

  The conductive cloth can also be used as a wearable sensor that is comfortable and does not feel cramped.

  In the process of the present invention, the preparation of the nanoparticles is preferably carried out by simultaneously (1) wetting the cloth with the reducing solution and (2) adding the metal salt solution, so that the nanoparticles are formed and the fibers Precipitate on top. This is an important conceptual advantage in that it is not necessary to immerse the entire fabric in a solution containing nanoparticles for nanoparticle precipitation. This method of nanometal deposition is more cost effective than conventional methods. Furthermore, this method can be adapted to selectively deposit silver. This is also possible by screen printing or spray printing on fabric for any type of circuit design, including complex patterns.

  Other types of polymers can be used to coat the fabric prior to depositing the nanoparticles. The polymers can also have a charge and can be used alone or in combination. In addition, the process can be utilized to cover cotton textiles with other types of nanoparticles that give different properties, such as copper, titanium dioxide and zinc.

  Different types of nanoparticles / nanowires can also be used prior to electroless plating. Electroless plating can be achieved with other types of materials depending on the application, such as Al, Ni and Sn.

  Another development of this process can include spray coating.

In a second aspect of the invention:
(I) providing a fiber having a negative charge on the surface of the fiber;
(Ii) treating the fiber with an alkaline solution to increase the negative charge on the surface of the fiber;
(Iii) applying a material to the fibers of step (ii) to provide a layer of said material around the fibers and changing the charge on the surface of the fibers from negative to positive;
(Iv) depositing a metal on the surface of the fiber of step (iii) to make the surface conductive, a method for producing a conductive fiber is provided.

  In a third aspect of the present invention, the method comprises first applying a reducing agent (such as aqueous sodium borohydride) to the surface of the fiber, and secondly applying a metal ion (such as silver nitrate) to the surface of the fiber, Thereby, metal ions are reduced to metal particles (preferably with an average size of less than 50 nm, most preferably with an average size of about 20 nm), the metal on the surface of the fiber having a positive charge on the surface of the fiber. A method for precipitating is provided.

  Preferably, the amount of reducing agent used is less than 7 mg (most preferably 6.1 mg) in 98 ml of water.

  Several preferred embodiments of the present invention will now be described with reference to the following accompanying drawings.

Figure 2 is a series of scanning electron microscope (SEM) images (three times reduction) of a cotton fabric treated by the method according to the present invention. FIG. 3 is a series of SEM images (three times reduction) of a cotton fabric treated by the method according to the present invention (except that the mercerizing step is omitted). It is a series of SEM images (three times reduction) of a cotton fabric treated by the method according to the present invention (except that the step of applying a cationic polyelectrolyte is omitted). Fig. 2 is a schematic diagram showing the steps of a preferred method according to the present invention. FIG. 4 is an SEM image (and enlarged view) of another cotton fabric treated by the method according to the present invention. FIG. 4 is an SEM image (and enlarged view) of another cotton fabric treated by the method according to the present invention. 2 is a photograph of a conductive path (in use) made by a method according to the invention. It is a SEM image of the cotton fiber immersed in the nano silver solution (not according to the present invention). It is a photograph of the cotton fabric of FIG. 8A after copper electroless plating.

Example 1
The cotton fabric was treated by the following four steps.
1. Mercer processing 2. Surface modification 3. Preparation, deposition and sintering of silver nanoparticles Lamination of Second Conductive Layer A schematic diagram showing this embodiment is shown in FIG.

1. Mercerization Cotton fabric was treated with 1 wt% aqueous NaOH for 30 minutes at room temperature followed by rinsing with distilled water.

2. Surface modification The sample was dried and then the fiber was coated with 0.198 wt% poly-diallyldimethylammonium chloride (PDADMAC) aqueous solution. This aqueous solution was made by taking 1 g of a 20 wt% solution of PDADMAC and mixing with 100 ml of water, so the resulting solution was 0.2 g PDADMAC in 101 ml of water, ie 0.198 wt%.

  After the fabric was completely wetted with the solution, the fabric was dried in an oven at 59 ° C. for 5 minutes in order to evaporate any remaining water molecules. Note that the fabric can be naturally dried at room temperature before the nanoparticles are deposited.

3. Preparation and Precipitation A 0.025M (0.43 g / 100 ml water) aqueous silver nitrate solution was prepared. Next, a cotton cloth (1.5 g, surface area of 64 mm ² ) was wetted with 0.1 ml of 1.61 × 10 ⁻⁴ M (6.1 mg / 98 ml of water) NaBH ₄ aqueous solution. Next, 10 μl of silver nitrate solution was added to the fabric.

  The fabric color quickly changed from white to brownish, indicating the formation of nanosilver particles. It was confirmed by dynamic light scattering (DLS) that the size of the nanoparticles was about 20 nm. The textile was dried at 59 ° C. and then another reduction step was performed to add another layer of nanoparticles to the fabric. The cotton fibers were completely covered with silver nanoparticles after three consecutive reductions.

4). Lamination of the second conductive layer A conductive silver sheath having a thickness of less than 100 nm was formed on the fibers, and then the conductive layer was thickened using electroless metal plating. Specifically, copper electroless plating was performed at a temperature of 46 ° C. for 25 minutes. The copper thickness was about 1.25 microns and the specific resistance was 0.1 Ω / sq.

  A series of SEM images of the resulting treated cotton fibers is shown in FIG.

  As a control, the method is applied to the same cotton fabric, but the mercerizing step is omitted. During subsequent process steps, the fibers were not completely covered with nanosilver particles (see FIG. 2). The mercerization process creates many more negative sites on the fiber, and without this step there is less chance of bonding in subsequent steps.

  Another control is performed by applying the method to the same cotton fabric without any PDADMAC.

  PDADMAC plays an important role as a binder between silver particles and textiles, resulting in a more uniform and dense coating (Figure 1). In contrast, the textile prepared using the mercerization step but without PDADMAC had an irregular morphology (Figure 3).

Example 2
To make a second sample of conductive fabric, the steps of Example 1 above were repeated, but instead of PDADMAC, the fabric was coated with an aqueous solution of poly (acrylamide-co-diallyldimethylammonium chloride) (PAADADMAC). Excluded points.

  The polymer solution was made by taking 1 g of a 10% by weight solution of PAADADMAC and mixing with 100 ml of water.

  The SEM image (Figure 5) showed that the fibers in the fabric were completely covered. Copper electroless plating was performed at a temperature of 46 ° C. for 25 minutes. As a result, a copper thickness of about 1.25 microns and a specific resistance of 0.2Ω / sq were obtained.

Example 3
Example 1 was repeated, but using a different cationic polyelectrolyte, namely poly (allylamine hydrochloride) (PAAHC) (molecular weight 58000, purchased from Sigma Aldrich).

  The polymer solution was prepared by preparing a 1% by weight PAAHC aqueous solution.

  The SEM image (Figure 6) showed that the fibers in the fabric were covered. Copper electroless plating was performed at a temperature of 46 ° C. for 25 minutes. As a result, a copper thickness of about 1.25 microns was obtained, and the specific resistance was 0.2Ω / sq.

Example 4
An experiment was conducted to investigate the addition of the polymer electrolyte to the nanoparticle solution prior to nanoparticle deposition on the fabric. The following steps were performed.

(A) 1 ml of 0.025M silver nitrate solution was added to 100 ml of 1.61 × 10 ⁻⁴ M NaBH ₄ solution. The formation of silver nanoparticles immediately changed the color to a yellow hue.
(B) An aqueous solution of poly-diallyldimethylammonium chloride (PDADMAC) is made by taking 1 g of a 20 wt% solution of PDADMAC and mixing it with 100 ml of water, so that the resulting solution is 0.2 g in 101 ml of water. PDADMAC of 0.198% by weight.
(C) 0.1 ml of the PDADMAC solution prepared in step (b) was added to the silver nanoparticle solution. The color changed from yellow to red. The solution was then centrifuged at 3500 rpm for 100 minutes. The spill was drained and the precipitate was used to coat the fabric, after which the textile was dried at 60 ° C. before copper electroless plating. By this method, a very thin conductive path could be made. One such conductive path is shown in FIG.

  Note that when the polyelectrolyte was added to the nanoparticle solution, the zeta potential of the solution changed from negative to positive (+36). In addition, after centrifugation, the particles were not agglomerated and no large silver metal particles were formed. While not wishing to be bound by theory, it is believed that this is due to the bond between the nanosilver particles and the charged groups on the polymer chain. Thus, when placed on the fabric, the nanosilver particles were uniformly adsorbed by the fabric.

Comparative Example 5
An experiment was conducted to investigate the effectiveness of the nano silver particle solution for producing conductive fabrics. The fibers in the fabric were coated with a PDADMAC linker. The nanosilver solution was prepared about 2 hours before application. Even after depositing the nanosilver particle solution eight times in succession, it was observed that the fabric was not coated with nanosilver particles. An SEM image of cotton fibers immersed in the nanosilver solution is shown in FIG. 8A.

  Furthermore, when copper electroless plating was performed at a temperature of 46 ° C. for more than 3 hours, the cloth was not covered with copper (see FIG. 8B). This is not surprising because the nanosilver coating was inadequate.

Comparative Example 6
The same steps as described above (see Example 1) were used to make a sample of conductive fabric. However, the only change made to the process was that the fabric was coated with a 1 wt% (% w) aqueous solution of chitosan (purchased from Sigma Aldrich).

  Note that chitosan does not dissolve in water. Therefore, an aqueous solution of (1 gram of chitosan and 2 ml acetic acid in 98 ml deionized water) was made.

  The obtained conductive cloth lost its stretchability, and the surface was quite granular and rough. The resistance value was equivalent to the resistance value of the fabric of Example 1.

  Since the texture of the textile changed so much, we decided to investigate using a diluted chitosan solution. However, similar results were observed when the chitosan solution was diluted to 0.1 wt% (% w).

Claims (19)

(A) providing a fiber having a negative charge on the surface of the fiber;
(B) applying a non-chitosan material (hereinafter referred to as a “linker”) to the fiber to provide a layer of the material on the fiber to change the charge on the surface of the fiber from negative to positive; ,
(C) making the surface of the fiber conductive using a metal, wherein the metal of step (c) is provided in the form of metal ions, and the metal ions are reduced to elemental metals. , and a step seen including,
The linker is a cationic polyelectrolyte;
A method for producing conductive fibers.   Reducing the metal ion to the elemental metal using a reducing agent, the reducing agent is first applied to the surface of the fiber, and the metal ion is applied second to the surface of the fiber; The method of claim 1.   The method of claim 1, wherein a solution of metal ions, a reducing agent and the material are combined and then the combination is applied to the fiber.   4. The method of claim 3, wherein the solution of metal ions and the reducing agent are first combined and then the substance is added. After step (a)
The method according to any one of claims 1 to 4, further comprising the step of (a1) treating the fiber with an alkali or acidic solution to increase the negative charge on the surface of the fiber. The method of claim 5, wherein step (a1) comprises treating the fiber with an aqueous sodium hydroxide solution having a concentration of less than 3.0 moldm ⁻³ . The method of claim 6, wherein the aqueous sodium hydroxide solution has a concentration of 1 % by weight. The substance of step (b) is protamine sulfate, polybrene, poly (L-lysine), poly (allylamine hydrochloride), poly (ethylene glycol-co-dimethylaminoethyl methacrylate), poly (ethyleneimine), polyacrylamide , Poly (acrylamide-co-diallyldimethylammonium chloride), diallyldimethylammonium chloride, poly (diallyldimethylammonium chloride), quaternized poly [bis (2-chloroethyl) ether-alt-1,3-bis [3- ( The method according to any one of claims 1 to 7 , which is dimethylamino) propyl] urea], polyquaternium-7, or any combination thereof. 2. The material of step (b) is poly (diallyldimethylammonium chloride), poly (acrylamide-co-diallyldimethylammonium chloride), poly (allylamine hydrochloride), or any combination thereof. 9. The method according to any one of 8 . The material of step (b) is a poly (diallyldimethylammonium chloride) 0 . The method according to claim 9 , which is a 2% by weight aqueous solution. The method according to any one of claims 1 to 10 , wherein the metal after reduction is in the form of metal particles having an average diameter of less than 50 nm. Reducing the metal ions into the metal of the element by using sodium borohydride, a method according to any one of claims 1 to 11. Wherein the metal ions are provided in the form of a metal nitrate, a method according to any one of claims 1 to 12. Wherein the metal is silver, the method according to any one of claims 1 to 13. And (d) an additional step of sintering the metal A method according to any of claims 1 to 14. The method according to claim 15 , wherein the sintering step (d) is performed at a temperature of 50 to 70 ° C. Comprising the additional step of applying another layer of metal to the metal on the fibers, the method according to any of claims 1 to 16. The method of claim 17 , wherein the further layer of metal is applied by electroless plating. The method of claim 18 , wherein the metal in the another layer is different from the metal of step (c).

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